Urban Forest Water Resources

A collaborative effort is underway to promote the benefits of using green infrastructure to protect drinking water supplies and public health, mitigate overflows from combined and separate sewers, and reduce stormwater pollution. Thank you for your interest in finding solutions to urban water quality, supply, and protection issues.



Ultimately, conservation is about empowering citizens to improve the communities where they live and work. The Alliance for Community Trees is the only national organization working to improve the urban forests where 80% of Americans live- our cities, towns, and villages. ACT’s national office assembles coalitions that drive broad environmental success for our more than 180 organizations in 41 states in the pursuit of Clean Air, Green Streets, and Healthy Neighborhoods.
Urban forestry is simply about trees in places where people live.
The U.S. Environmental Protection Agency has identified over $300 billion for nonintegrated water supply and wastewater projects for U.S. cities in the next 20 years. Those single-purpose projects will, for the most part, serve as Band-Aids without improving other related problems facing the cities that build them. On the other hand, this massive investment- informed by integrated approaches- can leverage funds to solve multiple problems and profoundly improve the quality of life of urban residents.
By incorporating green infrastructure with stormwater best management practices such as swales, retention grading, cisterns, infiltrators, and strategically-planted trees in building and landscaping designs, a multitude of benefits can be realized, including:

  • Improved water quality
  • Decreased risk of flooding
  • Reduced need for water importation
  • Heat-island effect mitigation
  • Reduction in contributions to global climate change
  • Recharged local groundwater
  • Improved water quality- Trees Help Cities Meet Clean Water Regulations
    Paved areas, which account for 20 to 40 percent of a city’s surface, pollute. They harbor exhaust-spewing cars, absorb and radiate heat, and collect contaminants that are eventually washed into the ground through rainwater runoff. Tree cover in urban areas can not only reduce cities’ costs for stormwater management but also help them improve water quality. Software such as CITYgreen uses scientific research and time-tested engineering practices to help city managers meet every tightening water quality regulations. Researchers at the Center for Urban Forest Research, Virginia Tech, Cornell University, and the University of California at Davis found that even going so far as to use engineered or structural soil can do a lot to minimize runoff from pavement. Made with natural and locally available materials, the aggregate can filter storm water as well as provide a better soil bed for trees, which offer shade, scrub the air of emissions, reduce ambient temperatures, and intercept rainfall. The vision, said McPherson is for landscape architects and engineers to think of the soil and the trees as mini reservoir system designed to filter a quantifiable amount of water and air.
    Decreased risk of flooding
    Trees are a cost effective way to reduce stormwater- exactly what is necessary with increased imperviousness. Community forests function as nonstructural stormwater management facilities.
    Casey Trees recently released the results of a year long study modeling the stormwater impacts of greening scenarios, including enhanced tree canopy and the increased use of green roofs in the District of Columbia. For an average year, the “Green Build-out” or high-end scenario prevented over 1.2 billion gallons of stormwater from entering the sewer system resulting in a reduction of 10 percent or over one billion gallons in discharge volumes to DC’s rivers and a 6.7 percent reduction in cumulative CSO frequency (74 discharges). The model also showed that the city could achieve up to a 54% reduction in stormwater runoff within several high volume sewersheds. A separate effort is underway to design a green system that retains 100% runoff from a 25-year storm event.
    Reduced need for water importation
    Pesticides are in the nation’s streams and ground water. Nearly 45 percent of our nation’s water bodies remain polluted, due in significant part to stormwater runoff and non-point source pollution linked to poor land use management. Communities across America are coping with the results of poorly planned, scattered, high-impact development, which consumes an ever-increasing share of our resources and contributes to water quality degradation in our rivers, streams, lakes, shores, and groundwater. The use of pesticides to control weeds, insects, and other pests has resulted in a range of benefits, including increased food production and reduction of insect-borne disease, but has also had adverse effects on water quality. While this is at concentrations seldom likely to affect humans, that is not the case for aquatic life and fish-eating wildlife (which we then eat).
    More locally, urban lawns- which cover a greater land area than any one agricultural crop in the U.S.- can produce surprising quantities of nitrates, phosphates, and organic chemicals. Every time rain falls on an urban development, it washes off oils, litter, sediment, fertilizers, and foreign chemicals from streets, parking lots, lawns, dumpster pads, and metal roofs. Knowledgeable design of urban development can solve the problem of runoff quality at the source– in the land uses where pollutants are first generated and rain water first touches the ground. The solution is embedded in transportation, land use, soil and vegetation, and only secondarily requires separate engineering structures.
    Heat-island effect mitigation
    From suburban driveways to the sprawling lots around big retailers, Americans devote lots of space to parking spaces. This growing land-use trend plays a role in heating up urban areas and adding to water pollution. Vast expanses of parking lots help raise urban temperatures. Purdue University researchers surveyed the total area devoted to parking in a midsize Midwestern county and found that parking spaces outnumbered resident drivers 3-to-1 and outnumbered resident families 11-to-1. The researchers found the total parking area to be larger than 1,000 football fields, or covering more than two square miles. Paved parking lots can generate heat, raising the surrounding areas air temperature and the temperature of the first flush of stormwater, creating significant ecological impacts. In Washington, the City of Olympia’s Public Works Department found that parking lots account for 53% of imperviousness on a commercial site and 15% of multi-family sites.
    Reduction in contributions to global climate change
    Human Health effects from air pollution usually involve respiratory functions and can be quite severe, but a UNICEF report now finds that as climate change worsens access to clean water is becoming more difficult. In addition, we are coming to understand the evidence on the economic impacts of climate change itself, as well as the economics of stabilizing greenhouse gases in the atmosphere in pursuit of a a low-carbon economy.
    Recharged local groundwater
    We are paving our way to water shortages. The summer of 2002 will be remembered for putting Americans from coast to coast through one of the worst droughts in decades. While experts discussed the links between water shortages, erratic weather conditions, and population growth, a largely overlooked problem was how development patterns are exacerbating problems with both water quality and quantity. Increases in impervious surface cover from sprawling development impair the landscape’s ability to recharge aquifers and surface waters. Trees increase soil permeability and facilitate groundwater recharge. In 2003, the National Association of Local Government Environmental Professionals, Trust for Public Land, and ERG put out a study to help communities address the water quality impacts of sprawl. Their findings reinforce the value of trees and links between urban forestry and stormwater management.
    These are just some of the benefits that are possible when urban sites are allowed to work in concert with nature and, together, create a sharp improvement in the quality of life in the neighborhoods in which we live, learn, work, and play. Rather than relying only on studies to prove this, urban forestry organizations around the country are constructing tangible projects that enable public agency staff, policymakers, and the public to see these projects at work, and then to imagine them scaled-up to the citywide or countywide level. Demonstration sites have helped initiate an ongoing process of significant changes in local and state agency missions, funding policies, designs, projects, plans, and programs.
    For example in Washington, DC, American Forests and Casey Trees helped area governments reduce the need for additional stormwater retention structures by 949 million cubic feet. In addition, they found that the city’s trees save the region $4.74 billion in gray infrastructure costs per 30-year construction cycle.
    At this moment, the nation wants action to secure real solutions to urban water quality, action that goes beyond buzzwords such as green and sustainable. Healthy urban forests are key to helping our growing cities and towns to support their water resources.
    Find Out More:
    Center for Watershed Protection
    Post-Construction Manual
    Urban Watershed Forestry Manual
    Storm Retrofit Best Practices
    Better Site Design Handbook
    Tales from the Urban Forest
    Watershed 263
    Fish Grow on Trees
    The Chesapeake Bay

    The Alliance for Community Trees is a 501(c)3 tax exempt organization (EIN # 68-0319301), and also participates in the Combined Federal Campaign (CFC # 12402). To discuss planned giving opportunities, call us at 301-277-0040.


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